In digital telephony, a code composed of a reserved binary number that is sent instead of an actual sound sample value from the CODEC when the incoming voice volume is below a certain level (i.e., when there is no sound). Depending on the transmission system used, the silence code is used for two purposes: (a) to allow other (lower priority) users to use that time-slot and (b) to produce a standard presence noise for the receiver. [Mattila]